Triazine ring based polymers for photoinduced liquid crystal alignment, liquid crystal alignment layer containing the same, liquid crystal element using the alignment layer and method of manufacturing the same

ABSTRACT

Triazine ring based polymers for photoinduced liquid crystal alignment introduces photoactive groups for inducing, reinforcing, improving and preserving liquid crystal alignment, for example photoreactor such as cinnamate, coumarin, chalcone and maleimide, as a chain to have at least one photoactive group. One of the photoactive groups can experience Fries rearrangement which induces liquid crystal alignment, and other groups can experience photodimerization, photoisomerization, photocrosslinkng or photodegradation to reinforce, change or preserve the generated alignment.

TECHNICAL FIELD

The present invention relates to triazine ring based polymers forphotoinduced liquid crystal alignment and a liquid crystal alignmentlayer using the polymers, and more particularly to polymers forphotoinduced liquid crystal alignment which has at least one photoactivechromophore in which a side chain having a photoactive group forinducing liquid crystal alignment and reinforcing, improving andpreserving the alignment of the liquid crystal is introduced to aprinciple chain of the polymer, and a liquid crystal layer using thepolymers.

BACKGROUND ART

A polymer for photoinduced liquid crystal alignment is used as an agentfor liquid crystal alignment of a device using optical characteristicsof the liquid crystal. Generally, the polymer for photoinduced liquidcrystal means materials which are able to align a liquid crystal bycoating a polymer on a substrate and then irradiating ultraviolet rayson its surface to form anisotrophy thereon.

A liquid crystal element using the polymer for liquid crystal alignmentis used in various fields including a liquid crystal display, acompensator, optical parts and so on. Thus, though the followingdescription is focused on a display element, it should be understoodthat the liquid crystal alignment layer is not limitedly used for thedisplay element but able to be applied to various fields describedabove.

Flat Panel Display (FPD) elements applied to a liquid crystal displaydevice gradually substitute for existing Cathode Ray Tubes (CRT), sincethe elements are thin and light and capable of scaling-up. Among theseFPDs, a Liquid Crystal Display (LCD) leads the FPD market at presentbecause it is advantageous in the facts that it is convenient to carryand consumes low power. In addition, the application of this LCD isbroadened to not only calculator and notebook computer but alsowall-mounted television and High Definition Television (HDTV).

In order to realize an image with liquid crystal elements, the liquidcrystal should be aligned to a predetermined direction on an interfacebetween the liquid crystal and a transparent conductive glass so thatthe liquid crystal is switched between the transparent conductiveglasses owing to an outside electric field. A degree of this liquidcrystal alignment is a most important fact for determining the imagequality of the ICDs.

Conventionally, there are known three representative methods foraligning a liquid crystal. A first method is a rubbing method shown inFIG. 1, which coats a polymer compound such as polyimide on a substrateand then rubs its surface with a rubbing drum around which a clothhaving flock-printed nylon, polyester or rayon fibers is wrapped. Asecond method is a SiO deposition which deposits SiO on a substrate toan inclined direction. A third method is an alignment method which coatspolymers for photoinduced liquid crystal alignment on a substrate andthen irradiates a light to a perpendicular or inclined direction inorder to cause photoreaction of the coated photopolymer material so thatthe anisotrophy is formed on its surface.

According to the first method, when rubbing the surface of the polymercompound with the rubbing drum, there are generated minute dusts orelectric discharge due to static electricity, which may cause manyproblems in the liquid crystal panel manufacturing process. According tothe second method, the deposition angle to the substrate and theuniformity of a film thickness are hardly maintained, and the processcan be enlarged to a large scale. According to the third method, thereare problems that a physical coherence between the photoinduced liquidcrystal alignment polymer and the liquid crystal is too week and thealignment is weakened due to the heat, which makes the method not bebrought into practice.

The liquid crystal alignment using the third method among them isdeveloped to align the liquid crystal by inducing a photoreaction of thephotopolymer using light irradiation and thus forming anisotrophy on thecoating surface. This alignment method is a non-contact treatment methodfor the alignment surface and has a feature that the overall process iskept clean since static electricity, dusts or other contaminantparticles are not generated. The possibility of the photo-alignment isrevealed using an azobenzene compound (K. Ichimura et al. Langmuir, 4,1214, 1988), and afterward various kinds of polymer compounds such aspolymaleimide (H.J.Choi et al. U.S. Patent No. 6,218,501) and polyolefin(R.H.Herr et al. U.S. Patent No. 6,201,087) are developed as aphoto-alignment material.

However, in order to put the photo-alignment method to practical use,there are needed improvement of photochemical stability, thermalstability and electrooptical properties and a large amount ofultraviolet rays. Therefore, there is needed the development of a newphoto-alignment material to solve such problems.

DISCLOSURE OF INVENTION

The present invention relates to a non-contact liquid crystal alignmentmethod using light irradiation which may align a liquid crystal intomulti domains with solving the problems of the conventional contact-typerubbing method and the conventional contact-type SiO deposition. Anobject of the invention is to provide a new photo-alignment materialwhich shows superior alignment characteristic, excellent thermal andoptical stability and improved electrooptical properties for the liquidcrystal.

In other words, the present invention provides a polymer forphotoinduced liquid crystal alignment which has at least one photoactivechromophore by using a triazine derivative as a principle chain of thepolymer and then introducing a side chain having a photoactive group forinducing alignment of the liquid crystal to the polymer chain andreinforcing, improving and preserving the alignment of the liquidcrystal. Fires rearrangement which induces alignment of the liquidcrystal may happen in one of the photoactive groups, whilephotodimerization, photoisomerization, photocrosslinking orphotodegradation for the purpose of reinforcement, changing orpreserving of the generated alignment may happen in other groups.

In addition, another object of the present invention is to provide aliquid crystal alignment layer using the polymer for photoinduced liquidcrystal alignment.

Other objects and advantages of the present invention are describedbelow, and would be better understood using the following embodiments ofthe invention. In addition, objects and advantages of the presentinvention can be realized by means and their associations revealed inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of preferredembodiments of the present invention will be more fully described in thefollowing detailed description, taken accompanying drawings. In thedrawings:

FIG. 1 is a side view for illustrating a conventional alignment processof a liquid crystal alignment layer; and

FIG. 2 is a schematic perspective view showing the alignment process ofa liquid crystal alignment layer according to the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

First of all, terms and words used in the specification and the claimsshould be interpreted not in a limited normal or dictionary meaning, butto include meanings and concepts conforming with technical aspects ofthe present invention, based on the face that inventors mayappropriately define a concept of a term to describe his/her owninvention in a best way.

Therefore, the configurations described in the specification and drawnin the figures are just most preferred embodiments of the presentinvention, not to show all of the technical aspects of the presentinvention. So, it should be understood that there might be variousequalities and modifications to be replaced with them.

A polymer for photoinduced liquid crystal alignment provided in thepresent invention includes a polymer having at least one photoactivegroup.

First Embodiment

In the first embodiment, a general formula of this polymer is as shownin Chemical Formula 1.

In the Chemical Formula 1, R₁ is selected from (1a) to (4a) in thefollowing Chemical Formula 2.

In (1 a) of the Chemical Formula 2, X is one selected from the followingChemical Formula 3.

In addition, in (1a) of the Chemical Formula 2, Y is one selected fromthe following Chemical Formula 4.

In the above Chemical Formula 4, the numerals 1, 2, 3, 4, 5, 6, 7, 8 or9 is one selected from the following Chemical Formula 5.

In (2a) and (3a) of the Chemical Formula 2, n is 0˜10, and the numerals1, 2, 3, 4 and 5 are respectively selected from the following ChemicalFormula 6.

In (4a) of the Chemical Formula 2, Y is one selected from the followingChemical Formula 7.

In (4a) of the Chemical Formula 2, the numerals 1 and 2 are respectivelyselected from the following Chemical Formula 8.

In the above Chemical Formula 1, R₂ and R₃ are respectively based on oneamine selected from the following Chemical Formula 9.

In addition, in the above Chemical Formula 1, R₄ and R₅ are respectivelybased on one carboxylic acid derivative or carboxylic acid dianhydrideselected from the following Chemical Formula 10.

In the present invention, the chemical linkages between R₂, R₃ and R₄,R₅ (i.e., between R₂ and R₄, R₂ and R₅, R₃ and R₄, and R₃ and R₅) in thechemical formula 1 can be amide linkage, imide linkage or their mixturerespectively.

The first embodiment of the invention is described based on the amidelinkage formation.

In the Chemical Formula 1, the linkage between R₂, R₃ and R₄, R₅ (i.e.,between R₂ and R₄, R₂ and R₅, R₃, and R₄ and R₃ and R₅) is performed bythe amide linkage formation obtained by the reaction of amine andcarboxylic acid, which is generally represented with the followingReaction Formula 1.

In the reaction formula 1, R and R¹ are organic groups respectively. Asshown in the above amide product, R is derived from amine compound,which is related to R₂ or R₃ in the chemical formula 1. Additionally, R′is derived from carboxylic acid compound, which is related to R₄ or R₅in the chemical formula 1.

R₂ and R₃ of the above Chemical Formula 1 are amine moietiesrespectively derived from one selected from the group consisting of thefollowing Chemical Formula 11.

In addition, R₄ and R₅ of the above Chemical Formula 1 are carboxylicacid moieties respectively derived from one selected from the groupconsisting of the following Chemical Formula 12.

In addition, any benzene ring structure included in R₁, R₂, R₃, R4 andR₅ in the polymer of the Chemical Formula 1, which represented by theChemical Formulas 2 to 12, may have not only the above-described para-structure but also ortho-, meta- structure or a mixing structure ofortho-, meta- and para-.

The polyamide polymer represented by the above Chemical Formula 1according to the first embodiment of the present invention has at leastone photoactive group. One of the photoactive groups may experiencephotodegradation, another group may experience Fires rearrangement andother groups may experience photodimerization, photoisomerization orphotocrosslinking for the purpose of reinforcement, changing orpreserving of the generated alignment.

An agent for liquid crystal alignment including the polymer representedby the Chemical Formula 1 according this embodiment can be used to makea liquid crystal alignment layer containing the polymer by coating thepolymer on a substrate and then irradiating ultraviolet rays thereon. Inparticular, the polymer for photoinduced liquid crystal alignment maychange a pretilt angle of the liquid crystal which is arranged accordingto a pretilt angle of the irradiated ultraviolet rays. The polymer alsomakes the pretilt angle of the liquid crystal to 0° by changing chemicalstructure or manipulating an irradiation angle of the ultraviolet rays.

Thus, Liquid Crystal Display (LCD) made using the polymer forphotoinduced liquid crystal alignment can be applied to various modessuch as SIN (Super Twisted Nematic), TN (Twisted Nematic), IPS (In PlaneSwitching), VA (Vertical Alignment) and VATN (Vertically Aligned TwistedNematic).

In addition, a liquid crystal element endowed with the liquid crystalalignment by the liquid crystal alignment layer can be used in variousapplications such as compensator or optical parts as well as the LCD.

Hereinafter a method of making a liquid crystal alignment layer usingthe polymer for photoinduced liquid crystal alignment of the firstembodiment is described in detail.

First Process

1˜20 wt % of a liquid crystal alignment agent having the polymer of thepresent embodiment expressed by the chemical formula 1 is dissolved intoan organic solvent to have viscosity of 1˜100 cps, and then the agent iscoated on a substrate in a thickness of 10˜500 nm to form an alignmentlayer.

The organic solvent is selected from chlorobenzene, N-methyl-pyrrolidone(NMP), N-ethyl-pyrrolidone (NEP), N,N-dimethyl-imidazolidone (DMI),N,N-dipropyle-imidazolidone (DPI), dimethyl-formamide (DMF),dimethyl-acetamide (DMAc), dimethyl-sulfoxide (DMSO), cyclopentanon,cyclohexanon, dichloro-ethane, butyl-cellusolve, γ-butyroactone andtetra-hydrofuran, or their mixture.

The liquid crystal alignment agent solved in the organic solvent iscoated on a substrate such as an ITO glass substrate in a predeterminedthickness in a range of 10˜500 nm in order to form a layer. At thistime, the coating process can be executed using any of possibleconventional ways such as spin coating and roll printing.

Second Process

Irradiate ultraviolet rays on the surface of the alignment layer coatedwith the liquid crystal alignment agent obtained in the first process inorder to make a liquid crystal alignment layer containing the polymer.At this time, to make the liquid crystal alignment layer, ultravioletrays linearly polarized using a polarizer or unpolarized ultravioletrays without using a polarizer are obliquely or perpendicularlyirradiated.

Hereinafter, the first embodiment is described in more detail with theuse of more concrete embodiments. The following embodiments are used forexemplifying concrete realization modes of the present invention, andthey should be not interpreted to limit or restrict the scope of theinvention.

Embodiment 1—1

A polyamide polymer for photoinduced liquid crystal alignment having acinnamate chromophore

(1) Reforming of Triazine Ring

27.1 g of 4(2-tetrahydropyranyl methoxy)bromobenzene is dissolved into250 ml of anhydrous tetrahydrofuran in three-neck flask filled withnitrogen, and then after inserting 3 g of magnesium, it is stiired for24 hours. This solution is reacted at −20° C. for 12 hours in athree-neck flask filled with nitrogen while slowly dropping 18.4 g ofcyanuric chloride into 200 ml of anhydrous tetrahydrofuran.

After the reaction, the reaction solution is decompressed at a roomtemperature to remove the tetrahydrofuran, and then dissolved inethylacetate. After mixing this solution with basic solution andseverely agitating it to extract impurities, aqueous phase is separatedand removed from the solution, and then the solution is decompressed ata room temperature to remove ethylacetate.

The solid phase material remaining after the removal of solvent isrecrystallized in n-hexane to obtain2-(4-(2-tetrahydropyranylmethoxy)phenyl)-4,6-dichloro- 1,3, 5-triazine.

(2) Introduction of a Hydroxy Functional Group into a Triazine Ring

After putting 34.0 g of the material obtained in (1) of the embodiment1-1 into a round bottom flask and then dissolving it with 300 ml oftetrahydrofuran, 0.3 g of pyridinum-paratoluene-sulfonate isadditionally put into the flask and 50 ml of ethanol is added forreaction during 24 hours.

After the reaction, the solvent is removed by distillation under reducedpressure, and then remained solids are dissolved again bymethylene-chloride and then blended with distilled water in a separatingfunnel to extract impurities twice. Calcium chloride is put into themethylene chloride solution to remove water, and then the solvent isremoved again through distillation under reduced pressure. This solidphase is recrystallized in a mixed solvent of methylene chloride andn-hexane to obtain 2-(4-hydroxyphenyl)-4,6-dichloro-1, 3, 5-triazine.

(3) Synthesis of a Triazine Ring Having Cinnamate Side Chain

Put 25.6 g of the triazine derivative obtained in (2) of the embodiment1—1 into a round bottom flask filled with nitrogen and then dissolve itby putting 200 ml of anhydrous tetrahydrofuran. After adding 15.2 g oftriethylaniine to this solution and then lowering the temperature of thesolution to −5° C., the solution is severely stirred and reacted for 12hours with slowly dropping a cinnamoyl chloride solution diluted byputting 100 ml of anhydrous tetrahydrofuran into 25 g of cinnamoylchloride.

After the reaction, the reacted solution is distilled under reducedpressure to remove tetrahydrofuran, and then the solution is dissolvedby methylene chloride, passes through a filter filled with silica gelsand is then distilled under reduced pressure to remove the solvent.

Finally, after recrystallization in an 1:1 mixed solvent of methylenechloride and n-hexane, the solution is filtered under reduced pressure.The obtained solid phase material is dried under vacuum to obtain atriazine having a cinnamate side chain.

(4) Synthesis of a Triazine Monomer Having Diamine Functional Group

38.6 g of the triazine derivative obtained in a way of (3) of theembodiment 1—1 is put into a round bottom flask and dissolved by 400 mlof chloroforum. 32.8 g of 4-aminophenol and 12 g of sodium hydroxide aredissolved in 300 ml of distilled water to which 3 g ofcetyltrimethylammonium bromide is dissolved, and then they are mixedwith the above triazine derivative solution and severely stirred andreacted for 24 hours. After the reaction, organic solution phase isseparated, and the reacted solution is moved to a separating funnel andwashed three times with distilled water to extract impurities, and thenwater is removed by calcium chloride. The solution is distilled underreduced pressure to remove chloroform which is an organic solvent, andthen recrystallized in a mixed solvent of methylene chloride andn-hexane.

The deposited crystal is filtered under reduced pressure and then driedunder vacuum to obtain a triazine monomer.

(5) Polymerization of Polyamide Polymer for Photoinduced Liquid CrystalAlignment Having a Cinnamate Functional Group

53.156 g of the triazine monomer obtained in the way of (4) of theembodiment 1—1 is put into a round bottom flask filled with nitrogen anddissolved by 400 ml of anhydrous tetrahydrofuran, and then 20.238 g oftriethyine is added to the solution. 20.3 g of terephthaloyl chloride isdissolved in 100 ml of anhydrous tetrahydrofuran, and then with slowlydropping it into the above-mentioned solution in which the triazinemonomer and triethylamine are dissolved, the solution is severelystirred and reacted for 12 hours.

After the reaction, the reaction solution is slowly poured into methanolfor precipitation, filtering and drying a deposit under vacuum. Theprocess for dissolving the obtained deposit again in tetrahydrofuran andthen precipitating in methanol is repeated twice, and then it is driedunder vacuum to obtain synthesized polyamide polymer for liquid crystalalignment having a cinnamate photoinduced functional group with the useof a triazine ring.

(6) Fabrication of a Liquid Crystal Display Cell

The obtained photoalignment agent is dissolved in a mixed solution ofNMP and butylcellusolve to have a density of 8 wt %, and then passesthrough a filtration membrane having a pore size of 0.1 μn so as toeliminate impurity particles. This solution is printed in a thickness ofabout 300 nm on a glass substrate coated with transparent electrodes forthe purpose of coating the photoalignment agent, and then the glasssubstrate is dried during about 1 hour at about 200° C. in order toremove the solvent. Then, complex photoreactions such asphotopolymerization of cinnamate group or photodegradation of polymerchain are induced to the glass substrate by irradiating ultraviolet raysof 500 W mercury lamp to the glass substrate one time per 2 seconds˜10minutes at an oblique angle of 20°, thereby making a liquid crystalalignment layer containing polymer. Spacers having a size of 4˜5 μn aresprayed on two glass substrates, and then the glass substrates areattached using epoxy adhesive to have a cell gap of 4˜5 μm. This cellexperiences a hardening process at 130° C. for 1 hour in order to hardenthe epoxy adhesive, so a cell in which two glass substrates areabsolutely adhered is manufactured. Liquid crystal is injected into themanufactured cell, and the cell experiences one time a heat treatmentprocess for heating at 100˜130° C. during 1 hour and then cooling to anambient temperature. Then, a liquid crystal display cell is finallyobtained.

Embodiment 1-2

A polyamide polymer for photoinduced liquid crystal alignment having achalcone chromophore

(1) Synthesis of Chalcone Functional Group

10 g of methoxy chalcone and 2.05 g of sodium cyanide are dissolved into100 ml of dimethyl-sulfoxide, and then reacted for 24 hours. After thereaction, the reacted solution is mixed with chloroform and agitatedtogether with distilled water so as to extract impurities. Afterremoving the solution phase, the solution is decompressed at a roomtemperature in order to eliminate chloroform. After recrystallization ofthe remained solid phase in methanol, the solution is dried undervacuum, thus obtaining 4-hydroxychalcone for photoreaction.

(2) Introduction of a Hydroxy Functional Group into a Triazine Ring

23.8 g of 4-hydroxychalcone synthesized in a way of (1) of theembodiment 1-2 is put into a round bottom flask filled with nitrogen andthen dissolved in 240 ml of anhydrous tetrahydrofuran. 2.4 g of sodiumhydride (NaH) is added to the solution and reacted at a room temperaturefor 6 hours. The solution is reacted at −5° C. for 24 hours by severelystirring with slowly dropping into a solution which is made by putting18.4 g of cyanuric chloride into a round bottom flask and thendissolving it into 200 ml of anhydrous tetrahydrofuran as mentioned in(1) of the embodiment 1-1 . After the reaction, tetrahydrofuran isremoved by distillation under reduced pressure, and then remained solidsare dissolved again into chloroform. This solution is washed three timeswith distilled water at a separating funnel to extract impurities, andthen water is removed by calcium chloride. The solution is thendistilled under reduced pressure to remove chloroform, and thenrecrystallized with a mixed solvent of methylene chloride and n-hexane.The recrystallized material is filtered under reduced pressure and thendried under vacuum to obtain triazine derivative having chalconefunctional group.

(3) Synthesis of a Triazine Monomer having Diamine Functional Group

38.6 g of the triazine derivative having a chalcone functional groupsynthesized in a way of (2) of the embodiment 1-2 is put into a roundbottom flask and dissolved by 300 ml of chloroform. 32.8 g of4-aminophenol and 12 g of sodium hydroxide are dissolved in 300 ml ofdistilled water to which 3 g of cetyltrimethylammonium bromide isdissolved, and then they are mixed with the above triazine derivativesolution and severely reacted for 24 hours. After the reaction, organicsolution phase is separated and moved to a separating funnel and washedthree times with distilled water to extract impurities. And then, wateris removed by calcium chloride. The solution free from water isdistilled under reduced pressure to remove chloroform which is anorganic solvent, and then recrystalized in a mixed solvent of methylenechloride and n-hexane. The deposited crystal is filtered under reducedpressure and then dried under vacuum to obtain a triazine monomer.

(4) Polymerization of Polyamide Polymer for Photoinduced Liquid CrystalAlignment having a Chalcone Chromophore

53.15 g of the triazine monomer obtained in the way of (3) of theembodiment 1-2 Is put into a round bottom flask filled with nitrogen anddissolved by 400 ml of anhydrous tetrahydrofuran, and then 20.24 g oftriethylamine is added to the solution. 20.3 g of terephthaloyl chlorideis dissolved in 100 ml of anhydrous tetrahydrofuran, and then withslowly dropping it into the above-mentioned solution in which thetriazine monomer and triethylamine are dissolved, the solution isseverely stirred and reacted for 12 hours. After the reaction, thereaction solution Is slowly poured into methanol for precipitation,filtering and drying a deposit under vacuum. The process for dissolvingthe obtained polymer again in tetrahydrofuran and then precipitating inmethanol is repeated twice, and then it is dried under vacuum to finallyobtain synthesized polyamide polymer for photoinduced liquid crystalalignment having a chalcone functional group with the use of a triazinering.

(5) Fabrication of a Liquid Crystal Display Cell

A liquid display cell is made in a way of (6) of the embodiment 1-1 byuse of the polyamide polymer for photoinduced liquid crystal alignmentobtained in a way of (4) of the embodiment 1-2.

Embodiment 1-3

A polyamide polymer for photoinduced liquid crystal alignment having acoumarin chromophore

(1) Introduction of a Coumarin Chromophore

16.2 g of 7-hydroxycoumarin and 2.4 g of sodium hydride (NaH) are putinto a round bottom flask filled with nitrogen, and then they aredissolved into 160 ml of anhydrous tetrahydrofiuran. After that, thesolution is severely stirred and reacted for 6 hours. This solution isseverely stirred and reacted for 24 hours at −5° C. with slowly droppingit into a solution which is made by putting 18.4 g of cyanuric chlorideinto a round bottom flask and then dissolving it into 200 ml ofanhydrous tetrahydrofuran as mentioned in (1) of the embodiment 1-1.After the reaction, tetrahydrofuran is removed by distillation underreduced pressure, and then remained solids are dissolved again intochloroform. This solution is washed three times with distilled water ata separating funnel to extract impurities, and then water is removed bycalcium chloride. The solution is then distilled under reduced pressureto remove chloroform, and then recrystallized with a mixed solvent ofmethylene chloride and n-hexane. The recrystallized material is filteredunder reduced pressure and then dried under vacuum to obtain triazinederivative having a coumarin functional group.

(2) Synthesis of a Triazine Monomer having Diamine Functional Group

31.1 g of the triazine derivative having a coumarin photoinducedfunctional group synthesized in a way of (1) of the embodiment 1-3 isput into a round bottom flask and dissolved by 300 ml of chloroform.32.8 g of 4-aminophenol and 12 g of sodium hydroxide are dissolved in300 ml of distilled water to which 3 g of cetyltrimethylammonium bromideis dissolved, and then they are mixed with the above triazine derivativesolution and severely reacted for 24 hours. After the reaction, organicsolution phase is separated and moved to a separating funnel and washedthree times with distilled water to extract impurities. And then, wateris removed by calcium chloride. The solution free from water isdistilled under reduced pressure to remove chloroform which is anorganic solvent, and then recrystalized in a mixed solvent of methylenechloride and n-hexane. The deposited crystal is filtered under reducedpressure and then dried under vacuum to obtain a triazine monomer.

(3) Polymerization of Polyamide Polymer for Photoinduced Liquid CrystalAlignment having a Coumarin Chromophore

45.54 g of the triazine monomer obtained in the way of (2) of theembodiment 1-3 is put into a round bottom flask filled with nitrogen anddissolved by 400 ml of anhydrous tetrahydrofuran, and then 20.24 g oftriethylanmine is added to the solution. 20.3 g of terephthaloylchloride is dissolved in 100 ml of anhydrous tetrahydrofuran, and thenwith slowly dropping it into the above-mentioned solution in which thetriazine monomer and triethylamine are dissolved, the solution isseverely stirred and reacted for 12 hours. After the reaction, thereaction solution is slowly poured into methanol for precipitation,filtering and drying a deposit under vacuum. The process for dissolvingthe obtained polymer again in tetrahydrofuran and then precipitating inmethanol is repeated twice, and then it is dried under vacuum to finallyobtain synthesized polyamide polymer for photoinduced liquid crystalalignment having a coumarin functional group with the use of a triazinering.

(4) Fabrication of a Liquid Crystal Display Cell

A liquid display cell is made in a way of (6) of the embodiment 1-1 byuse of the polyamide polymer for photoinduced liquid crystal alignmentobtained in a way of (3) of the embodiment 1-3.

Experimental Example: Measurement of Liquid Crystal Display CellCharacteristics

Electro-optical characteristic, thermal stability, optical stability,residual DC and VHR characteristics of the liquid crystal display cellsmade in a way of the embodiments 1-1 to 1-3 are measured, and itsresults are expressed in Tables 1, 2, 3 and 4.

Test 1: Change of a Pretilt Angle Depending on Thermal Treatment

As seen in the following Table 1, the polymer for photoinduced liquidcrystal alignment of the embodiments have thermal stability, opticaltransparency and excellent coating ability, which are basiccharacteristics of conventionally used polyimide, together with superiormechanical characteristics which is peculiar to polyamide polymer. Thus,in case of making a photoalignment liquid crystal cell by use of thepolymer for liquid crystal alignment according to the embodiments, amulti domain liquid crystal alignment can be easily obtained by simpleprocesses. In addition, owing to dramatically improved alignmentcharacteristics, for example that the pretilt angle of the liquidcrystal is kept even after the seal baking which needs a hightemperature, the cell can be applied to a liquid crystal displayrequiring high definition and wide viewing angle.

TABLE 1 Embodiment Embodiment Embodiment 1-1 1-2 1-3 Process Lightirradiation Light irradiation Light irradiation Density 8 wt % 8 wt % 8wt % Pretilt Angle Room 0˜5° 0˜3° 0˜4° Temperature After 0˜5° 0˜3° 0˜4°Thermal Treatment Contrast Ratio 195 190 190 Note 1. The pretilt angleis measured using a crystal angle rotation manner. Note 2. The heattreatment is executed for 3 minutes at 150° C. which is a seal bakingtemperature.Test 2: Thermal Stability

Thermal stability of the liquid crystal cell is measured as follows.After measuring an initial pretilt angle of the liquid crystal cell, achange of the pretilt angle depending on time is measured at a roomtemperature with thermal-aging the liquid crystal cell at 150° C. Incase the thermal stability of alignment is unstable, the pretilt anglechanges depending on time, while when stable, the pretilt angle hardlychanges. Results of the test are expressed in the following Table 2. Aswell understood from Table 2, the photoalignment agents according to theembodiments have so excellent thermal stability to keep the alignmentand the pretilt angle of the liquid crystal stably even during long timethermal aging, thereby satisfying basic characteristics for a liquidcrystal display.

TABLE 2 Embodiment Embodiment Embodiment 1-1 1-2 1-3 Pretilt Angle ˜5°   ˜4°  ˜4° Thermal Aging 150° C. 150° 150° Temperature Thermal Aging 48hours 48 hours 48 hours Time Pretilt Angle No No No ChangeTest 3: Optical Stability

The liquid crystal cells are made according to the embodiments 1-1, 1-2and 1-3 and their optical stability is measured. For the measurement ofoptical stability, light in a range of ultraviolet and visible rays isirradiated on the alignment surface of one cell, and then a change ofthe alignment characteristics is check by the eyes with the use of apolarizer for irradiated surface and non-irradiated surface. Themeasurement results are expressed in the following Table 3. In case thecell has insufficient optical stability, the light irradiated to aliquid crystal cell induces a change of the liquid crystal alignmentcharacteristic on the irradiated surface. Thus, the alignmentcharacteristic of the irradiated surface is significantly changeddifferent from that of the non-irradiated surface or destroyed so thatthe liquid crystal alignment is mingled unspecificably. Therefore, thiscell showing a change of the alignment characteristic cannot be used asa display device.

TABLE 3 Embodiment Embodiment Embodiment 1-1 1-2 1-3 Amount of 0.5 J/cm²No Change No Change No Change Irradiated   1 J/cm² No Change No ChangeNo Change Light   2 J/cm² No Change No Change No Change Angle of 90° NoChange No Change No Change Irradiated 80° No Change No Change No ChangeLight 70° No Change No Change No ChangeTest 4: Residual DC and Voltage Holding Ratio(VHR)

A DC voltage is applied to both ends of the liquid crystal cell withchanging in a range of −10 V˜10 V and its electrostatic capacitance ismeasured. The residual DC is obtained from a size of the hystereticvalue of the electrostatic capacitance. The liquid crystal cell is aTN-structure specimen having a thickness of 4˜6 μm and preparedaccording to the manufacturing methods specified in the above-mentionedembodiments 1-1 to 1-3. Two electrodes of the prepared liquid crystalcell is connected to an LCD meter (i.e., Fluke 6306), and a change ofits electrostatic capacitance at 1 kHz is recorded with changing the DCvoltage from 0 V to 10 V, 0 V and −10 V. Hysteresis of the electrostaticcapacitance change depending on the voltage is obtained and used formeasuring a residual DC. In order to obtain the voltage holding ratio(VHR), pulses having a duration of 64 μs in ±1 Volt, 60 Hz period areapplied and then a ratio that a voltage initially applied is maintainedis measured. Its results are shown in the following Table 4. As seen inTable 4, the measurement results show low residual DC in a range of10˜13 mV at 20° C., and high VHR in a range of 98˜99%, for all of threecells. This shows that the photoalignment agent according to theembodiments 1-1 to 1-3 satisfies the basic characteristics capable ofbeing used as a liquid crystal display device.

TABLE 4 Embodiment Embodiment Embodiment 1-1 1-2 1-3 R-DC 20° C. 10 mV11 mV 13 mV 60° C. 30 mV 35 mV 33 mV VHR 20° C. 99% 99% 98% 60° C. 98%96% 97%Second Embodiment

In the second embodiment, a general formula of the polymer is as shownin Chemical Formula 13.

In the Chemical Formula 13, R₁ is identical to that of the firstembodiment.

However, in the Chemical Formula 13, the imide linkage connecting R₂, R₃to R₄, R₅ (i.e., R₂ to R₄, R₂ to R₅, R₃ to R4, and R₃ to R₅) is obtainedby the reaction of amine and carboxylic acid dianhydride, which isgenerally represented with the following Reaction Formula 2.

In the reaction formula 2, R and R′ are organic groups respectively. Asshown in the above imide product, R is derived from amine compound,which is related to R₂ or R₃ in the Chemical Formula 13. Additionally,R′ is derived from carboxylic acid dianhydride compound, which isrelated to R₄ or R₅ in the Chemical Formula 13.

R₂ and R₃ of the above Chemical Formula 13 are amine moietiesrespectively derived from one selected from the group consisting of thefollowing Chemical Formula 14.

In addition, R₄ and R₅ of the above Chemical Formula 13 are carboxylicacid dianhydride moieties respectively derived from one selected fromthe group consisting of the following Chemical Formula 15.

In addition, the benzene ring structure included in R₁, R₂, R₃, R₄ andR₅, represented by the Chemical Formulas 2 to 8, 14 and 15, in thepolymer of the Chemical Formula 13 may have not only the above-describedpara-structure but also ortho- or meta-structure or a mixing structureof ortho-, meta- and para-.

The polyimide polymer represented by the above Chemical Formula 13according to this embodiment of the present invention has at least onephotoactive group, as in the case of the first embodiment. One of thephotoactive groups may experience photodegradation, another group mayexperience Fires rearrangement, and other groups may experiencephotodimerization, photoisomerization or photocrosslinking for thepurpose of reinforcement, changing or preserving of the generatedalignment.

An agent for photoinduced liquid crystal alignment including the polymerrepresented by the Chemical Formula 13 according this embodiment hassubstantially identical characteristics and applications to the firstembodiment.

In addition, a method for making a liquid crystal alignment layer by useof the polyimide polymer for photoinduced liquid crystal alignmentaccording to this embodiment is substantially identical to the methodfor making a liquid crystal alignment layer by use of the polyamidepolymer for photoinduced liquid crystal alignment according to the firstembodiment.

Hereinafter, the second embodiment is described in more detail with theuse of more concrete embodiments. The following embodiments are used forexemplifying concrete realizing modes of the present invention, and theyshould be not interpreted to limit or restrict the scope of theinvention.

Embodiment 2-1

A polyimide polymer for photoinduced liquid crystal alignment having acinnamate chromophore.

(1) Reforming of Triazine Ring

27.1 g of 4(2-tetrahydropyranyl methoxy)bromobenzene is dissolved into250 ml of anhydrous tetrahydrofuran in three-neck flask filled withnitrogen, and then made to react upon 3 g of magnesium for 24 hours.This solution is reacted at −20° C. for 12 hours in a three-neck flaskfilled with nitrogen while slowly dropping 18.4 g of cyanuric chlorideinto 200 ml of anhydrous tetrahydrofuran.

After the reaction, the reaction solution is decompressed at a roomtemperature to remove the tetrahydrofuran, and then dissolved inethylacetate. After mixing this solution with basic solution andseverely agitating it to extract impurities, aqueous phase is separatedand removed from the solution, and then the solution is decompressed ata room temperature to remove ethylacetate.

The solid phase material remaining after the removal of solvent isrecrystallized in n-hexane to obtain2-(4-(2-tetrahydropyranylmethoxy)phenyl)-4, 6-dichloro- 1, 3,5-triazine.

(2) Introduction of a Hydroxy Functional Group into a Triazine

Ring

After putting 34.0 g of the material obtained in (1) of the embodiment2-1 into a round bottom flask and then dissolving it with 300 ml oftetrahydrofuran, 0.3 g of pyridinum-paratoluene-sulfonate isadditionally put into the flask and 50 ml of ethanol is added forreaction during 24 hours.

After the reaction, the solvent is removed by distillation under reducedpressure, and then remained solids are dissolved again bymethylene-chloride and then blended with distilled water in a separatingfunnel to extract impurities twice. Calcium chloride is put into themethylene chloride solution to remove water, and then the solvent isremoved again through distillation under reduced pressure. This solidphase is recrystallized in a mixed solvent of methylene chloride andn-hexane to obtain 2-(4-hydroxyphenyl)-4, 6-dichloro- 1, 3, 5-triazine.

(3) Synthesis of a Triazine Ring Having Cinnamate Chromophore

Put 25.6 g of the triazine derivative obtained in (2) of the embodiment2-1 into a round bottom flask filled with nitrogen and then dissolve itby putting 200 ml of anhydrous tetrahydrofuran. After adding 15.2 g oftriethylamine to this solution and then lowering the temperature of thesolution to −50° C., the solution is severely stirred and reacted for 12hours with slowly dropping a cinnamoyl chloride solution diluted byputting 100 ml of anhydrous tetrahydrofuran into 25 g of cinnamoylchloride.

After the reaction, the reacted solution is distilled under reducedpressure to remove tetrahydrofuran, and then the solution is dissolvedby methylene chloride, passes through a filter filled with silica gelsand is then distilled under reduced pressure to remove the solvent.

Finally, after recrystallization in an 1:1 mixed solvent of methylenechloride and n-hexane, the solution is filtered under reduced pressure.The obtained solid phase material is dried under vacuum to obtain atriazine derivative having a cinnamate chromophore.

(4) Synthesis of a Triazine Monomer Having Diamine Functional Group

38.6 g of the triazine derivative obtained in a way of (3) of theembodiment 2-1 is put into a round bottom flask and dissolved by 400 mlof chloroform. 32.8 g of 4-aminophenol and 12 g of sodium hydroxide aredissolved in 300 ml of distilled water to which 3 g ofcetyltrimethylammonium bromide is dissolved, and then they are mixedwith the above triazine derivative solution and severely reacted for 24hours. After the reaction, organic solution phase is separated, and thereacted solution is moved to a separating funnel and washed three timeswith distilled water to extract impurities, and then water is removed bycalcium chloride. The solution is distilled under reduced pressure toremove chloroform which is an organic solvent, and then recrystallizedin a mixed solvent of methylene chloride and n-hexane.

The deposited crystal is filtered under reduced pressure and then driedunder vacuum to obtain a triazine monomer.

(5) Polymerization of Polyimide Polymer for Photoinduced Liquid CrystalAlignment Having a Cinnamate Functional Group

53.156 g of the triazine monomer obtained in the way of (4) of theembodiment 2-1 is put into a round bottom flask filled with nitrogen anddissolved by 400 ml of N-methyl-pyrrolidone. 21.8 g of 1, 2, 4,5-benzenetetracarboxylic acid dianhydride is dissolved in 100 ml ofN-methyl-pyrrolidone, and then with slowly dropping it into theabove-mentioned solution in which the triazine monomer are dissolved,the solution is severely stirred and reacted for 24 hours.

After the reaction, the reaction solution is slowly poured into methanolfor precipitation, filtering and drying a deposit under vacuum. Theprocess for dissolving the obtained polymer again inN-methyl-pyrrolidone and then precipitating in methanol is repeatedtwice, and then it is dried under vacuum to finally obtain synthesizedpolyamic acid which is a precursor of a polyimide polymer for liquidcrystal alignment having a cinnamate functional group with the use of atriazine ring.

(6) Fabrication of a Liquid Crystal Display Cell

The obtained photoalignment agent is dissolved in a mixed solution ofNMP and butylcellusolve to have a density of 8 wt%, and then passesthrough a filtration membrane having a pore size of 0.1 μm so as toeliminate impurity particles. This solution is printed in a thickness ofabout 300 nm on a glass substrate coated with transparent electrodes forthe purpose of coating the photoalignment agent, and then the glasssubstrate is dried during about 1 hour at about 200° C. in order toremove the solvent with completing imidization reaction. Then, complexphotoreactions such as photopolymerization of cinnamate group orphotodegradation of polymer chain are induced to the glass substrate byirradiating ultraviolet rays of 500 W mercury lamp to the glasssubstrate one time per 2 seconds˜10 minutes at an angle of 20°, therebymaking a liquid crystal alignment layer containing polymer. Spacershaving a size of 4˜5 μm are sprayed on two glass substrates, and thenthe glass substrates are attached using epoxy adhesive to have a cellgap of 4˜5 μm. This cell experiences a hardening process at 130° C. for1 hour in order to harden the epoxy adhesive, so a cell in which twoglass substrates are absolutely adhered is manufactured. Liquid crystalis injected into the manufactured cell, and the cell experiences onetime a heat treatment process for heating at 100˜130° C. during 1 hourand then cooling to an ambient temperature. Then, a liquid display cellis finally obtained.

Embodiment 2-2

A polyimide polymer for photoinduced liquid crystal alignment having achalcone chromophore

(1) Synthesis of Chalcone Chromophore

10 g of methoxy chalcone and 2.05 g of sodium cyanide are dissolved into100 ml of dimethyl-sulfoxide, and then reacted during 24 hours. Afterthe reaction, the reacted solution is mixed with chloroform and stirredtogether with distilled water so as to extract impurities. Afterremoving the solution phase, the solution is decompressed at a roomtemperature in order to eliminate chloroform. After recrystallizing theremained solid phase in methanol, the solution is dried under vacuum,thus obtaining 4-hydroxychalcone for photoreaction.

(2) Introduction of a Chalcone into a Triazine Ring

23.8 g of 4-hydroxchalcone synthesized in a way of (1) of the embodiment2-2 is put into a round bottom flask filled with nitrogen and thendissolved in 240 ml of anhydrous tetrahydrofuran. 2.4 g of sodiumhydride (NaH) is added to the solution and reacted at room temperaturefor 6 hours. The solution is reacted at −5° C. for 24 hours by severelystirring with slowly dropping into a solution which is made by putting18.4 g of triazine into a round bottom flask and then dissolving it into200 ml of anhydrous tetrahydrofuran as mentioned in (1) of theembodiment 2-1. After the reaction, tetrahydrofuran is removed bydistillation under reduced pressure, and then remained solids aredissolved again into chloroform. This solution is washed three timeswith distilled water at a separating funnel to extract impurities, andthen water is removed by calcium chloride. The solution is thendistilled under reduced pressure to remove chloroform, and thenrecrystallized with a mixed solvent of methylene chloride and n-hexane.The recrystallized material is filtered under reduced pressure and thendried under vacuum to obtain triazine derivative having chalconefunctional group.

(3) Synthesis of a Triazine Monomer Having Diamine Functional Group

38.6 g of the triazine derivative having a chalcone functional groupsynthesized in a way of (2) of the embodiment 2-2 is put into a roundbottom flask and dissolved by 400 ml of chloroform. In addition, 32.8 gof 4-aminophenol and 12 g of sodium hydroxide are dissolved in 300 ml ofdistilled water to which 3 g of cetyltrimethylammonium bromide isdissolved, and then they are mixed with the above triazine solution andseverely reacted for 24 hours. After the reaction, organic solutionphase is separated and moved to a separating funnel and washed threetimes with distilled water to extract impurities. And then, water isremoved by calcium chloride. The solution free from water is distilledunder reduced pressure to remove chloroform which is an organic solvent,and then recrystallized in a mixed solvent of methylene chloride andn-hexane. The deposited crystal is filtered under reduced pressure andthen dried under vacuum to obtain a triazine monomer.

(4) Polymerization of Polyimide Polymer for Photoinduced Liquid CrystalAlignment Having a Chalcone Functional Group

53.15 g of the triazine monomer obtained in the way of (3) of theembodiment 2-2 is put into a round bottom flask filled with nitrogen anddissolved by 400 ml of N-methyl-pyrrolidone. 21.8 g of 1, 2, 4,5-benzenetetracarboxylic acid dianhydride is dissolved in 100 ml ofN-methyl-pyrrolidone, and then with slowly dropping it into theabove-mentioned solution in which the triazine monomer are dissolved,the solution is severely stirred and reacted for 24 hours. After thereaction, the reaction solution is slowly poured into methanol forprecipitation, filtering and drying a polymer under vacuum. The processfor dissolving the obtained polymer again in N-methyl-pyrrolidone andthen precipitating in methanol is repeated twice, and then it is driedunder vacuum to finally obtain synthesized polyamic acid which is aprecusor of a polyimide polymer for photoinduced liquid crystalalignment having a chalcone functional group with the use of a triazinering.

(5) Fabrication of a Liquid Crystal Display Cell

A liquid display cell is made in a way of (6) of the embodiment 2-1 byuse of the polyimide polymer for photoinduced liquid crystal alignmentobtained in a way of (4) of the embodiment 2-2.

Embodiment 2-3

A polyimide polymer for photoinduced liquid crystal alignment having acoumarin chromophore

(1) Introduction of a Coumarin Chromophore

16.2 g of 7-hydroxycoumarin and 2.4 g of sodium hydride (NaH) are putinto a round bottom flask filled with nitrogen, and then they aredissolved into 160 ml of anhydrous tetrahydrofuran. After that, thesolution is severely stirred and reacted for 6 hours. This solution isseverely stirred and reacted for 24 hours at −5° C. with slowly droppingit into a solution which is made by putting 18.4 g of triazine into around bottom flask and then dissolving it into 200 ml of anhydroustetrahydrofuran as mentioned in (1) of the embodiment 2-1. After thereaction, tetrahydrofuran is removed by distillation under reducedpressure, and then remained solids are dissolved again into chloroform.This solution is washed three times with distilled water at a separatingfunnel to extract impurities, and then water is removed by calciumchloride. The solution is then distilled under reduced pressure toremove chloroform, and then recrystallized with a mixed solvent ofmethylene chloride and n-hexane. The recrystallized material is filteredunder reduced pressure and then dried under vacuum to obtain triazinederivative having a coumarin functional group.

(2) Synthesis of a Triazine Monomer Having Diamine Functional Group

31.1 g of the triazine derivative having a coumarin functional groupsynthesized in a way of (1) of the embodiment 2-3 is put into a roundbottom flask and dissolved by 300 ml of chloroform. 32.8 g of4-aminophenol and 12 g of sodium hydroxide are dissolved in 400 ml ofdistilled water to which 3 g of cetyltrimethylammonium bromide isdissolved, and then they are mixed with the above triazine solution andseverely reacted for 24 hours. After the reaction, organic solutionphase is separated and moved to a separating funnel and washed threetimes with distilled water to extract impurities. And then, water isremoved by calcium chloride. The solution is distilled under reducedpressure to remove chloroform which is an organic solvent, and thenrecrystallized in a mixed solvent of methylene chloride and n-hexane.The deposited crystal is filtered under reduced pressure and then driedunder vacuum to obtain a triazine monomer.

(3) Polymerization of Polyimide Polymer for Photoinduced Liquid CrystalAlignment Having a Coumarin Functional Group

45.54 g of the triazine monomer obtained in the way of (2) of theembodiment 2-3 is put into a round bottom flask filled with nitrogen anddissolved by 400 ml of N-methyl-pyrrolidone. 21.8 g of 1, 2, 4,5-benzenetetracarboxylic acid dianhydride is dissolved in 100 ml ofN-methyl-pyrrolidone, and then with slowly dropping it into theabove-mentioned solution in which the triazine monomer are dissolved,the solution is severely stirred and reacted for 24 hours. After thereaction, the reaction solution is slowly poured into methanol forprecipitation, filtering and drying a polymer under vacuum. The processfor dissolving the obtained polymer again in N-methyl-pyrrolidone andthen precipitating in methanol is repeated twice, and then it is driedunder vacuum to finally obtain synthesized polyamic acid which is aprecursor of a polyimide polymer for photoinduced liquid crystalalignment having a coumarin functional group with the use of a triazinering.

(4) Fabrication of a Liquid Crystal Display Cell

A liquid display cell is made in a way of (6) of the embodiment 2-1 byuse of the polyimide polymer for photoinduced liquid crystal alignmentobtained in a way of (3) of the embodiment 2-3.

Experimental Example: Measurement of Liquid Crystal Display CellCharacteristics

Electro-optical characteristic, thermal stability, optical stability,residual DC and VHR characteristics of the liquid crystal display cellsmade in a way of the embodiments 2-1 to 2-3 are measured, and itsresults are expressed in the tables 5, 6, 7 and 8.

Test 1: Change of a Pretilt Angle Depending on Thermal Treatment

As seen in the following table 5, the polymer for photoinduced liquidcrystal alignment of the embodiments have thermal stability, opticaltransparency and excellent coating ability, which are basiccharacteristics of conventionally used polyimide. In addition, sincehaving the functional group, the polymer has an advantage that an amountof irradiated light required for alignment is reduced in comparison tothe conventional polyimide alignment agent. Thus, in case of making aphotoalignment liquid crystal cell by use of the polymer for liquidcrystal alignment according to the embodiments, a multi domain liquidcrystal alignment can be easily obtained by simple processes. Inaddition, owing to dramatically improved alignment characteristics, forexample that the pretilt angle of the liquid crystal is kept even afterthe seal baking which needs a high temperature, the cell can be appliedto a liquid crystal display requiring high definition and wide viewingangle.

TABLE 5 Embodiment Embodiment Embodiment 2-1 2-2 2-3 Process Lightirradiation Light irradiation Light irradiation Density 8 wt % 8 wt % 8wt % Pretilt Angle Room 0˜4° 0˜4° 0˜4° Temperature After 0˜4° 0˜3° 0˜4°Thermal Treatment Contrast Ratio 195 190 190 Note 1. The pretilt angleis measured using a crystal angle rotation manner. Note 2. The heattreatment is executed for 3 minutes at 150° C. which is a seal bakingtemperature.Test 2: Thermal Stability

Thermal stability of the liquid crystal cell is measured as follows.After measuring an initial pretilt angle of the liquid crystal cell, achange of the pretilt angle depending on time is measured at a roomtemperature with thermal aging the liquid crystal cell at 200° C. Incase the thermal stability of alignment is unstable, the pretilt anglechanges depending on time, while when stable, the pretilt angle hardlychanges. Results of the test are expressed in the following table 6. Aswell understood from the table 6, the photoalignment agents according tothe embodiments have so excellent thermal stability to keep thealignment and the pretilt angle of the liquid crystal stably even duringlong time thermal aging, thereby satisfying basic characteristics for aliquid crystal display.

TABLE 6 Embodiment Embodiment Embodiment 2-1 2-2 2-3 Pretilt Angle ˜4°   ˜3°  ˜4° Thermal Aging 200° C. 200° 200° Temperature Thermal Aging 48hours 48 hours 48 hours Time Pretilt Angle No No No ChangeTest 3: Optical Stability

The liquid crystal cells are made according to the embodiments 2-1, 2-2and 2-3 and their optical stability is measured. For the measurement ofoptical stability, light in a range of ultraviolet and visible rays isirradiated on the alignment surface of one cell, and then a change ofthe alignment characteristics is check by the eyes with the use of apolarizer for irradiated surface and non-irradiated surface. Themeasurement results are expressed in the following table 7. In case thecell has insufficient optical stability, the light irradiated to aliquid crystal cell induces a change of the liquid crystal alignmentcharacteristic on the irradiated surface. Thus, the alignmentcharacteristic of the irradiated surface is significantly changeddifferent from that of the non-irradiated surface or destroyed so thatthe liquid crystal alignment is mingled unspecificably. Therefore, thiscell showing a change of the alignment characteristic cannot be used asa display device.

TABLE 7 Embodiment Embodiment Embodiment 2-1 2-2 2-3 Amount of 0.5 J/cm²No Change No Change No Change Irradiated   1 J/cm² No Change No ChangeNo Change Light   2 J/cm² No Change No Change No Change Angle of 90° NoChange No Change No Change Irradiated 80° No Change No Change No ChangeLight 70° No Change No Change No ChangeTest 4: Residual DC and Voltage Holding Ratio(VHR)

A DC voltage is applied to both ends of the liquid crystal cell withchanging in a range of −10 V˜10 V and its electrostatic capacitance ismeasured. The residual DC is obtained from a size of the hystereticvalue of the electrostatic capacitance. The liquid crystal cell is aTN-structure specimen having a thickness of 4˜6 μm and preparedaccording to the manufacturing methods specified in the above-mentionedembodiments 2-1 to 2-3. Two electrodes of the prepared liquid crystalcell is connected to an LCD meter (i.e., Fluke 6306), and a change ofits electrostatic capacitance at 1 kHz is recorded with changing the DCvoltage from 0 V to 10 V, 0 V and −10 V. Hysteresis of the electrostaticcapacitance change depending on the voltage is obtained and used formeasuring a residual DC. In order to obtain the voltage holding ratio(VHR), pulses having a duration of 64 μs in ±1 Volt, 60 Hz period areapplied and then a ratio that a voltage initially applied is maintainedis measured. Its results are shown in the following table 8. As seen inTable 8, the measurement results show low residual DC in a range of10˜13 mV at 20° C., and high VHR in a range of 98˜99%, for all of threecells. This shows that the photoalignment agent according to theembodiments 2-1 to 2-3 satisfies the basic characteristics capable ofbeing used as a liquid crystal display device

TABLE 8 Embodiment Embodiment Embodiment 2-1 2-2 2-3 R-DC 20° C.  8 mV10 mV 10 mV 60° C. 25 mV 30 mV 32 mV VHR 20° C. 99% 99% 98% 60° C. 99%98% 97%Third Embodiment

In the third embodiment, a general formula of the polymer is as shown inChemical Formula 16.

In the Chemical Formula 16, R₁ is identical to those of the firstembodiment and second embodiment.

In the Chemical Formula 16, the linkage connecting R₂, R₃ to R₄ (i.e.,R₂ to R₄ and R₃ to R₄) is performed by the amide linkage obtained by thereaction of amine and carboxylic acid, which is generally representedwith the following Reaction Formula 1.

In the Reaction Formula 1, R and R′ are organic groups respectively. Asshown in the above amide product, R is derived from amine compound,which is related to R₂ or R₃ in the Chemical Formula 16. Additionally,R′ is derived from carboxylic acid compound, which is related to R₄ inthe Chemical Formula 16.

In the Chemical Formula 16, the linkage connecting R₂, R₃ to R₅ (i.e.,R₂ to R₅ and R₃ to R₅)is performed by the imide linkage obtained by thereaction of amine and carboxylic acid dianhydride, which is generallyrepresented with the following Reaction Formula 2.

In the reaction formula 2, R and R′ are organic groups respectively. Asshown in the above imide product, R is derived from amine compound,which is related to R₂ or R₃ in the Chemical Formula 16. Additionally,R′ is derived from carboxylic acid dianhydride compound, which isrelated to R₅ in the Chemical Formula 16.

Thus, the imide and the amide linkage, which are linkages of theChemical Formula 16, are obtained by the reaction between amine and anyof carboxylic acid and carboxylic acid dianhydride, which arerepresented by the Reaction Formula 1 and 2 respectively.

R₂ and R₃ of the above Chemical Formula 16 are amine moietiesrespectively derived from one selected from the Chemical Formula 14respectively.

R₄ in the above Chemical Formula 16 is a carboxylic acid moiety selectedfrom the Chemical Formula 12. R₅ in the above Chemical Formula 16 iscarboxylic acid dianhydride moiety derived from one selected from theChemical Formula 15.

In addition, any benzene ring structure included in R₁, R₂, R₃, R₄ andR₅, represented by chemical formulas 2 to 8, 12, 14 and 15, in thepolymer of the Chemical Formula 16 may have not only the above-describedpara-structure but also ortho- or meta-structure or a mixing structureof ortho-, meta- and para-.

The poly(amide-imide) copolymer represented by the above ChemicalFormula 16 according to this embodiment of the present invention has atleast one photoactive group, as in the case of the first and secondembodiments. One of the photoactive groups may experiencephotodegradation, another group may experience Fires rearrangement, andother groups may experience photodimerization, photoisomerization orphotocrosslinking for the purpose of reinforcement, changing orpreserving of the generated alignment.

In addition, the poly(amide-imide) copolymer can be used as acompatibilizer for suppressing phase separation when the polyamidealignment agent and the polyimide alignment agent are used together.

An agent for photoinduced liquid crystal alignment including the polymerrepresented by the Chemical Formula 16 according this embodiment hassubstantially identical characteristics and applications to the firstembodiment.

In addition, a method for making a photoinduced liquid crystal alignmentlayer by use of the poly(amide-imide) copolymer for liquid crystalalignment according to this embodiment is substantially identical to themethod for making a liquid crystal alignment layer by use of thepolyamide polymer for photoinduced liquid crystal alignment according tothe first embodiment and the method for making a photoinduced liquidcrystal alignment layer by use of polyimide polymer for photoinducedliquid crystal alignment according to the second embodiment.

Hereinafter, the third embodiment is described in more detail with theuse of more concrete embodiments. The following embodiments are used forexemplifying concrete realizing modes of the present invention, and theyshould be not interpreted to limit or restrict the scope of theinvention.

Embodiment 3-1

A poly(amide-imide) polymer for photoinduced liquid crystal alignmenthaving a cinnamate chromophore

(1) Reforming of Triazine Ring

27.1 g of 4(2-tetrahydropyranyl methoxy)bromobenzene is dissolved into250 ml of anhydrous tetrahydrofuran in three-neck flask filled withnitrogen, and then made to react upon 3 g of magnesium for 24 hours.This solution is reacted at −20° C. for 12 hours in a three-neck flaskfilled with nitrogen while slowly dropping 18.4 g of cyanuric chlorideinto 200 ml of anhydrous tetrahydrofuran.

After the reaction, the reaction solution is decompressed at a roomtemperature to remove the tetrahydrofuran, and then dissolved inethylacetate. After mixing this solution with basic solution andseverely stirring it to extract impurities, aqueous phase is separatedand removed from the solution, and then the solution is decompressed ata room temperature to remove ethylacetate.

The solid phase material remaining after the removal of solvent isrecrystallized in n-hexane to obtain2-(4-(2-tetrahydropyranylmethoxy)phenyl)-4,6-dichloro-1,3,5-triazine.

(2) Introduction of a Hydroxy Functional Group Into a Triazine Ring

After putting 34.0 g of the material obtained in (1) of the embodiment3-1 into a round bottom flask and then dissolving it with 300 ml oftetrahydrofuran, 0.3 g of pyridinum-paratoluene-sulfonate isadditionally put into the flask and 50 ml of ethanol is added forreaction for 24 hours.

After the reaction, the solvent is removed by distillation under reducedpressure, and then remained solids are dissolved again bymethylene-chloride and then blended with distilled water in a separatingfunnel to extract impurities twice. Calcium chloride is put into themethylene chloride solution to remove water, and then the solvent isremoved again through distillation under reduced pressure. This solidphase is recrystallized in a mixed solvent of methylene chloride andn-hexane to obtain 2-(4-hydroxyphenyl)-4,6-dichloro-1,3,5-triazine.

(3) Synthesis of a Triazine Ring Having Cinnamate Chromophore

Put 25.6 g of the triazine derivative obtained in (2) of the embodiment3-1 into a round bottom flask filled with nitrogen and then dissolve itby putting 200 ml of anhydrous tetrahydrofuran. After adding 15.2 g oftriethylamine to this solution and then lowering the temperature of thesolution to −5° C., the solution is severely stirred and reacted for 12hours with slowly dropping a cinnamoyl chloride solution diluted byputting 100 ml of anhydrous tetrahydrofuran into 25 g of cinnamoylchloride.

After the reaction, the reacted solution is distilled under reducedpressure to remove tetrahydrofuran, and then the solution is dissolvedby methylene chloride, passes through a filter filled with silica gelsand is then distilled under reduced pressure to remove the solvent.

Finally, after recrystallization in a 1:1 mixed solvent of methylenechloride and n-hexane, the solution is filtered under reduced pressure.The obtained solid phase material is dried under vacuum to obtain atriazine derivative having a cinnamate side chain.

(4) Synthesis of a Triazine Monomer Having Diamine Functional Group

38.6 g of the triazine derivative obtained in a way of (3) of theembodiment 3-1 is put into a round bottom flask and dissolved by 400 mlof chloroform. 32.8 g of 4-aminophenol and 12 g of sodium hydroxide aredissolved in 300 ml of distilled water to which 3 g ofcetyltrimethylammonium bromide is dissolved, and then they are mixedwith the above triazine solution and severely reacted for 24 hours.After the reaction, organic solution phase is separated, and the reactedsolution is moved to a separating funnel and washed three times withdistilled water to extract impurities, and then water is removed bycalcium chloride. The solution free from water is distilled underreduced pressure to remove chloroform which is an organic solvent, andthen recrystallized in a mixed solvent of methylene chloride andn-hexane.

The deposited crystal is filtered under reduced pressure and then driedunder vacuum to obtain a triazine monomer.

(5) Polymerization of Poly(amide-imide) Polymer for Photoinduced LiquidCrystal Alignment Having a Cinnamate Functional Group

53.156 g of the triazine monomer obtained in the way of (4) of theembodiment 3-1 is put into a round bottom flask filled with nitrogen andthen dissolved by 400 ml of tetrahydrofuran. 10.12 g of triethylamin isadded to the solution.

After dissolving 10.15 g of terephthaloyl chloride in 100 ml ofanhydrous tetrahydrofuran, the solution is severely stirred and reactedfor 6 hours while slowly dropping it into a solution in which theabove-mentioned triazine monomer and triethylamine are dissolved. Thissolution is additionally reacted for 6 hours while slowly dropping asolution, in which 10.9 g of 1,2,4,5-benzenetetracarboxylic aciddianhydride is dissolved in 100 ml of N-methyl-pyrrolidone, into theabove solution.

After the reaction, the reaction solution is slowly poured into methanolfor precipitation, filtering and drying a polymer under vacuum. Theprocess for dissolving the obtained polymer again in tetrahydrofuran andthen preciptating in methanol is repeated twice, and then it is driedunder vacuum to finally obtain synthesized poly(amide-imide) copolymerfor photoinduced liquid crystal alignment having a coumarin functionalgroup with the use of a triazine ring.

(6) Fabrication of a Liquid Crystal Display Cell

The obtained photoalignment agent is dissolved in a mixed solution ofNMP and butylcellusolve to have a density of 8 wt %, and then passesthrough a filtration membrane having a pore size of 0.1 μm so as toeliminate impurity particles. This solution is printed in a thickness ofabout 300 nm on a glass substrate coated with transparent electrodes forthe purpose of coating the photoalignment agent, and then the glasssubstrate is dried during about 1 hour at about 200° C. in order toremove the solvent with completing imidization reaction. Then, complexphotoreactions such as photopolymerization of cinnamate group orphotodegradation of polymer chain are induced to the glass substrate byirradiating ultraviolet rays of 500 W mercury lamp to the glasssubstrate one time per 2 seconds˜10 minutes at an oblique angle of 20°,thereby making a liquid crystal alignment layer containing polymer.Spacers having a size of 4˜5 μm are sprayed on two glass substrates, andthen the glass substrates are attached using epoxy adhesive to have acell gap of 4˜5 μm. This cell experiences a hardening process at 130° C.for 1 hour in order to harden the epoxy adhesive, so a cell in which twoglass substrates are absolutely adhered is manufactured. Liquid crystalis injected into the manufactured cell, and the cell experiences onetime a heat treatment process for heating at 100˜130° C. during 1 hourand then cooling to an ambient temperature. Then, a liquid display cellis finally obtained.

Embodiment 3-2

A poly(amide-imide) polymer for photoinduced liquid crystal alignmenthaving a chalcone chromophore

(1) Synthesis of Chalcone Chromophore

10 g of methoxy chalcone and 2.05 g of sodium cyanide are dissolved into100 ml of dimethyl-sulfoxide, and then reacted during 24 hours. Afterthe reaction, the reacted solution is mixed with chloroform and stirredtogether with distilled water so as to extract impurities. Afterremoving the solution phase, the solution is decompressed at a roomtemperature in order to eliminate chloroform. After recrystallizing theremained solid phase in methanol, the solution is dried under vacuum,thus obtaining side chain 4-hydroxychalcone for photoreaction.

(2) Introduction of a Chalcone Functional Group into a Triazine Ring

23.8 g of 4-hydroxchalcone synthesized in a way of (1) of the embodiment3-2 is put into a round bottom flask filled with nitrogen and thendissolved in 240 ml of anhydrous tetrahydrofuran. 2.4 g of sodiumhydride (NaH) is added to the solution and reacted at a room temperaturefor 6 hours. The solution is reacted at −5° C. for 24 hours by severelystirring with slowly dropping into a solution which is made by putting18.4 g of triazine into a round bottom flask and then dissolving it into200 ml of anhydrous tetrahydrofuran as mentioned in (1) of theembodiment 3-1. After the reaction, tetrahydrofuran is removed bydistillation under reduced pressure, and then remained solids aredissolved again into chloroform. This solution is washed three timeswith distilled water at a separating funnel to extract impurities, andthen water is removed by calcium chloride. The solution is thendistilled under reduced pressure to remove chloroform, and thenrecrystallized with a mixed solvent of methylene chloride and n-hexane.The recrystallized material is filtered under reduced pressure and thendried under vacuum to obtain triazine derivative having chalconefunctional group.

(3) Synthesis of a Triazine Monomer having Diamine Functional Group

38.6 g of the triazine derivative having a chalcone functional groupsynthesized in a way of (2) of the embodiment 3-2 is put into a roundbottom flask and dissolved by 400 ml of chloroform. In addition, 32.8 gof 4-aminophenol and 12 g of sodium hydroxide are dissolved in 300 ml ofdistilled water to which 3 g of cetyltrimethylammonium bromide isdissolved, and then they are mixed with the above triazine solution andseverely reacted for 24 hours. After the reaction, organic solutionphase is separated and moved to a separating funnel and washed threetimes with distilled water to extract impurities. And then, water isremoved by calcium chloride. The solution is distilled under reducedpressure to remove chloroform which is an organic solvent, and thenrecrystallized in a mixed solvent of methylene chloride and n-hexane.The deposited crystal is filtered under reduced pressure and then driedunder vacuum to obtain a triazine monomer.

(4) Polymerization of Poly(amide-imide) Polymer for Photoinduced LiquidCrystal Alignment having a Chalcone Functional Group

53.15 g of the triazine monomer obtained in the way of (3) of theembodiment 3-2 is put into a round bottom flask filled with nitrogen anddissolved by 400 ml of anhydrous tetrahydrofuran. 10.12 g oftriethylamine is added to the solution. 10.15 g of terephthaloilchloride is dissolved in 100 ml of anhydrous tetrahydrofuran, and thenwith slowly dropping it into the above-mentioned solution in which thetriazine monomer and triethylamine are dissolved, the solution isseverely stirred and reacted for 24 hours. While dropping a solution, inwhich 10.9 g of 1,2,4,5-benzenetetracarboxylic acid dianhydride isdissolved in 100 ml of N-methyl-pyrrolidone, the above-mentionedsolution is additionally reacted for 6 hours. After the reaction, thereaction solution is slowly poured into methanol for precipitation,filtering and drying a polymer under vacuum. The process for dissolvingthe obtained polymer again in tetrahydrofuran and then precipitating inmethanol is repeated twice, and then it is dried under vacuum to finallyobtain synthesized poly(amide-imide) copolymer for photoinduced liquidcrystal alignment having a chalcone functional group with the use of atriazine ring.

(5) Fabrication of a Liquid Crystal Display Cell

A liquid display cell is made in a way of (6) of the embodiment 3-1 byuse of the poly(amide-imide) copolymer for photoinduced liquid crystalalignment obtained in a way of (4) of the embodiment 3-2.

Embodiment 3-3

A poly(amide-imide) polymer for photoinduced liquid crystal alignmenthaving a coumarin chromophore

(1) Introduction of a Coumarin Chromophore

16.2 g of 7-hydroxycoumarin and 2.4 g of sodium hydride (NaH) are putinto a round bottom flask filled with nitrogen, and then they aredissolved into 160 ml of anhydrous tetrahydrofuran. After that, thesolution is severely stirred and reacted for 6 hours. This solution isseverely stirred and reacted for 24 hours at −5° C. with slowly droppingit into a solution which is made by putting 18.4 g of triazine into around bottom flask and then dissolving it into 200 ml of anhydroustetrahydrofuran as mentioned in (1) of the embodiment 3-1. After thereaction, tetrahydrofuran is removed by distillation under reducedpressure, and then remained solids are dissolved again into chloroform.This solution is washed three times with distilled water at a separatingfunnel to extract impurities, and then water is removed by calciumchloride. The solution is then distilled under reduced pressure toremove chloroform, and then recrystallized with a mixed solvent ofmethylene chloride and n-hexane. The recrystallized material is filteredunder reduced pressure and then dried under vacuum to obtain triazinederivative having a coumarin functional group.

(2) Synthesis of a Triazine Monomer having Diamine Functional Group

31.1 g of the triazine derivative having a coumarin functional groupsynthesized in a way of (1) of the embodiment 3-3 is put into a roundbottom flask and dissolved by 300 ml of chloroform. 32.8 g of4-aminophenol and 12 g of sodium hydroxide are dissolved in 400 ml ofdistilled water to which 3 g of cetyltrimethylammonium bromide isdissolved, and then they are mixed with the above triazine solution andseverely reacted for 24 hours. After the reaction, organic solutionphase is separated and moved to a separating funnel and washed threetimes with distilled water to extract impurities. And then, water isremoved by calcium chloride. The solution is distilled under reducedpressure to remove chloroform which is an organic solvent, and thenrecrystallized in a mixed solvent of methylene chloride and n-hexane.The deposited crystal is filtered under reduced pressure and then driedunder vacuum to obtain a triazine monomer.

(3) Polymerization of Poly(amide-imide) Polymer for Photoinduced LiquidCrystal Alignment having a Coumarin Functional Group

45.54 g of the triazine monomer obtained in the way of (2) of theembodiment 3-3 is put into a round bottom flask filled with nitrogen anddissolved by 400 ml of tetrahydrofuran. 10.12 g of triethylamine isadded to the solution. 10.15 g of terephthaloyl chloride is dissolved in100 ml of anhydrous tetrahydrofuran, and then with slowly dropping itinto the above-mentioned solution in which the triazine monomer andtriethylamine are dissolved, the solution is severely stirred andreacted for 6 hours. While dropping a solution, in which 10.9 g of1,2,4,5-benzenetetracarboxylic acid dianhydride is dissolved in 100 mlof N-methyl-pyrrolidone, the above-mentioned solution is additionallyreacted for 6 hours. After the reaction, the reaction solution is slowlypoured into methanol for precipitation, filtering and drying a polymerunder vacuum. The process for dissolving the obtained polymer again intetrahydrofuran and then precipitating in methanol is repeated twice,and then it is dried under vacuum to finally obtain synthesized polyamicacid which is a precursor of a poly(amide-imide) copolymer forphotoinduced liquid crystal alignment having a coumarin functional groupwith the use of a triazine ring.

(4) Fabrication of a Liquid Crystal Display Cell

A liquid display cell is made in a way of (6) of the embodiment 3-1 byuse of the poly(amide-imide) copolymer for liquid crystal alignmentobtained in a way of (3) of the embodiment 3-3.

EXPERIMENTAL EXAMPLE Measurement of Liquid Crystal Display CellCharacteristics

Electro-optical characteristic, thermal stability, optical stability,residual DC and VHR characteristics of the liquid crystal display cellsmade in a way of the embodiments 3-1 to 3-3 are measured, and itsresults are expressed in the tables 9, 10, 11 and 12.

Test 1: Change of a Pretilt Angle depending on Thermal Treatment

As seen in the following table 9, the polymers for photoinduced liquidcrystal alignment of the embodiments have thermal stability, opticaltransparency and excellent coating ability, which are basiccharacteristics of conventionally used polyimide. Together with theexcellent characteristics, the liquid crystal alignment agent iscopolymerized with polyimide. In addition, since having thephotoreactive functional group, the polymer has an advantage that anamount of irradiated light required for alignment is reduced incomparison to the conventional polyimide alignment agent. Thus, in caseof making a photoalignment liquid crystal cell by use of the polymer forliquid crystal alignment according to the embodiments, a multi domainliquid crystal alignment can be easily obtained by simple processes. Inaddition, owing to dramatically improved alignment characteristics, forexample that the pretilt angle of the liquid crystal is kept even afterthe seal baking which needs a high temperature, the cell can be appliedto a liquid crystal display requiring high definition and wide viewingangle.

TABLE 9 Embodiment Embodiment Embodiment 3-1 3-2 3-3 Process Lightirradiation Light irradiation Light irradiation Density 8 wt % 8 wt % 8wt % Pretilt Angle Room 0˜3° 0˜5° 0˜6° Temperature After 0˜3° 0˜5° 0˜6°Thermal Treatment Contrast Ratio 196 194 193 Note 1. The pretilt angleis measured using a crystal angle rotation manner. Note 2. The Thermaltreatment is executed for 3 minutes at 150° C. which is a seal bakingtemperature.

Test 2: Thermal Stability

Thermal stability of the liquid crystal cell is measured as follows.After measuring an initial pretilt angle of the liquid crystal cell, achange of the pretilt angle depending on time is measured at a roomtemperature with Thermal-aging the liquid crystal cell at 200° C. Incase the thermal stability of alignment is unstable, the pretilt anglechanges depending on time, while when stable, the pretilt angle hardlychanges. Results of the test are expressed in the following table 10. Aswell understood from the table 10, the photoalignment agents accordingto the embodiments have so excellent thermal stability to keep thealignment and the pretilt angle of the liquid crystal stably even duringlong time thermal aging, thereby satisfying basic characteristics for aliquid crystal display.

TABLE 10 Embodiment Embodiment Embodiment 3-1 3-2 3-3 Pretilt Angle ˜3°  ˜5°  ˜6° Thermal Aging 150° C. 150° 150° Temperature Thermal Aging 48hours 48 hours 48 hours Time Pretilt Angle No No No Change

Test 3: Optical Stability

The liquid crystal cells are made according to the embodiments 3-1, 3-2and 3-3 and their optical stability is measured. For the measurement ofoptical stability, light in a range of ultraviolet and visible rays isirradiated on the alignment surface of one cell, and then a change ofthe alignment characteristics is check by the eyes with the use of apolarizer for irradiated surface and non-irradiated surface. Themeasurement results are expressed in the following table 11. In case thecell has insufficient optical stability, the light irradiated to aliquid crystal cell induces a change of the liquid crystal alignmentcharacteristic on the irradiated surface. Thus, the alignmentcharacteristic of the irradiated surface is significantly changeddifferent from that of the non-irradiated surface or destroyed so thatthe liquid crystal alignment is mingled unspecificably. Therefore, thiscell showing a change of the alignment characteristic cannot be used asa display device.

TABLE 11 Embodiment Embodiment Embodiment 3-1 3-2 3-3 Amount of 0.5J/cm² No Change No Change No Change Irradiated   1 J/cm² No Change NoChange No Change Light   2 J/cm² No Change No Change No Change Angle of90° No Change No Change No Change Irradiated 80° No Change No Change NoChange Light 70° No Change No Change No Change

Test 4: Residual DC and Voltage Holding Ratio(VHR)

A DC voltage is applied to both ends of the liquid crystal cell withchanging in a range of −10 V˜10 V and its electrostatic capacitance ismeasured. The residual DC is obtained from a size of the hystereticvalue of the electrostatic capacitance. The liquid crystal cell is aTN-structure specimen having a thickness of 4˜6 μm and preparedaccording to the manufacturing methods specified in the above-mentionedembodiments 3-1 to 3-3. Two electrodes of the prepared liquid crystalcell is connected to an LCD meter (i.e., Fluke 6306), and a change ofits electrostatic capacitance at 1 kHz is recorded with changing the DCvoltage from 0 V to 10 V, 0 V and −10 V. Hysteresis of the electrostaticcapacitance change depending on the voltage is obtained and used formeasuring a residual DC. In order to obtain the voltage holding ratio(VHR), pulses having a duration of 64 μs in ±1 Volt, 60 Hz period areapplied and then a ratio that a voltage initially applied is maintainedis measured. Its results are shown in the following table 12. As seen inTable 8, the measurement results show low residual DC in a range of10˜13 mV at 20° C., and high VHR in a range of 98˜00%, for all of threecells. This shows that the photoalignment agent according to theembodiments 3-1 to 3-3 satisfies the basic characteristics capable ofbeing used as a liquid crystal display device.

TABLE 12 Embodiment 3-1 Embodiment 3-2 Embodiment 3-3 R-DC 20° C.  9 mV12 mV 12 mV 60° C. 26 mV 28 mV 30 mV VHR 20° C. 99% 99% 99% 60° C. 99%98% 97%

INDUSTRIAL APPLICABILITY

As described above, the present invention provides polyamide, polyimideand poly(amide-imide) polymers for photoinduced liquid crystal alignmentfor photopolymerization and photolysis to which an optical reactiongroup such as cinnamate, coumarin, calcone and maleimide is introducedby using triazine derivatives as a main chain and an alignment layerusing the polymers, so the present invention may overcome the problemssuch as low thermal stability, poor alignment ability caused by weakphysical binding force between a liquid crystal and an alignment layerand susceptibility to the optical stability during a cell makingprocess, which are possessed by the conventional photoalignment agentusing a hydrocarbon polymer such as polyolefin as a main chain. Inaddition, the polymers according to the present invention may beprovided with not only optical transparency and chemical resistance butalso excellent mechanical properties and heat resistance which arepeculiar to polyamide, polyimide and poly(amide-imide) polymers. Thus,the liquid crystal display elements made using the polymer forphotoinduced liquid crystal alignment according to the present inventionmay realize high quality display.

Changes or modifications of the present invention can be easilyperformed to those skilled in the art, and it should be understood thatthose changes and modifications are included in the scope of the presentinvention.

1. A liquid crystal alignment agent containing triazine ring basedpolymer expressed by the following chemical formula (1):

wherein R₁ in the Chemical Formula (I) is one selected from thefollowing formula (1a) to (4a):

wherein X in the above formula (1a) is one selected from the followingformula:

wherein Y in the formula (1a) is one selected from the followingformula:

wherein the numerals 1, 2, 3, 4, 5, 6, 7, 8 or 9 in the above formulasis one selected from the following formula:

wherein in the above formula (2a) and (3a), n is 0˜10, and the numerals1, 2, 3, 4 and 5 are respectively selected from the following formula:

wherein Y in the above formula (4a) is one selected from the followingformula:

wherein the numerals 1 and 2 in the above formula (4a) are respectivelyselected from the following formula:

wherein R₂ and R3 in the Chemical Formula (I) are respectively based onone amine selected from the following formula:

wherein R4 and R₅ in the above Chemical Formula (I) are respectivelybased on one carboxylic acid derivative or carboxylic acid dianhydrideselected from the following formula:


2. A liquid crystal alignment agent according to claim 1, wherein R₄ andR₅ in the Chemical Formula (I) are carboxylic acid moieties respectivelyselected from the group consisting of the following formulas:


3. A liquid crystal alignment agent according to claim 1, wherein R₄ andR₅ in the Chemical Formula (I) are carboxylic acid dianhydride moietiesrespectively derived from one selected from the group consisting of thefollowing formulas:


4. A liquid crystal alignment agent according to claim 1, wherein R₄ inthe Chemical Formula (I) is a carboxylic acid moiety selected from thegroup consisting of the following formulas:

wherein R₅ in the Chemical Formula (I) is a carboxylic acid dianhydridemoiety derived from one selected from the group consisting of thefollowing formulas:


5. A liquid crystal alignment agent according to any of claims 1 to 4,wherein any benzene ring structure contained in R₁, R₂, R₃, R₄ and R₅ inthe Chemical Formula (I) has an ortho-structure, a meta-structure or apara-structure or a mixing structure thereof.
 6. A liquid crystalalignment layer containing a polymer, which is made by coating theliquid crystal alignment agent defined in any of the claims 1 to 4 on asubstrate to form an alignment layer and then irradiating ultravioletrays thereon.
 7. A liquid crystal element endowed with orientation byapplying a liquid crystal alignment which is made by coating the liquidcrystal alignment agent defined in any of the claims 1 to 4 on asubstrate to form an alignment layer and then irradiating ultravioletrays thereon.
 8. A liquid crystal element according to claim 7, whereinthe liquid crystal element is used for one of liquid crystal display,compensator and optical components.
 9. A liquid crystal elementaccording to claim 8, wherein the liquid crystal display has a drivingmode selected in the group consisting of STN (Super Twisted Nematic), TN(Twisted Nematic), IPS (In Plane Switching), VA (Vertical Alignment) andVATN (Vertically Aligned Tested Nematic).
 10. A method for making aliquid crystal alignment layer containing polymer, comprising the stepsof: forming an alignment layer by dissolving 1˜20 wt % of the liquidcrystal alignment agent defined in any of the claims 1 to 4 into anorganic solvent to have viscosity of 1˜100 cps and then coating theagent on a substrate in a thickness of 10˜500 nm; and irradiatingultraviolet rays, either polarized or unpolarized, on the surface of thealignment layer either obliquely or perpendicularly.
 11. A method formaking a liquid crystal alignment layer according to claim 10, whereinthe organic solvent is selected from the group consisting ofchlorobenzene, N-methyl-pyrrolidone (NMP), N-ethyl-pyrrolidone (NEP),N,N-dimethyl-imidazolidone (DMI), N,N-dipropyle-imidazolidone (DPI),dimethyl-formamide (DMF), dimethyl-acetamide (DMAc), dimethyl-sulfoxide(DMSO), cyclopentanon, cyclohexanon, dichloro-ethane, butyl-cellusolve,γ-butyroactone and tetra-hydrofuran, or their mixture.
 12. A liquidcrystal alignment agent containing triazine ring based polyimide polymerexpressed by the following chemical formula (II):

wherein R₁ in the Chemical Formula (II) is selected from the followingformula (1a) to (4a):

wherein X in the above formula (1a) is one selected in from thefollowing formula:

wherein Y in the formula (1a) is one selected from the followingformula:

wherein the numerals 1, 2, 3, 4, 5, 6, 7, 8 or 9 in the above formula isone selected from the following formula:

wherein, in the above formula (2a) and (3a), n is 0˜10, and the numerals1, 2, 3, 4 and 5 are respectively selected from the following formula:

wherein Y in the above formula (4a) is one selected from the followingformula:

wherein the numerals 1 and 2 in the above formula (4a) are respectivelyselected from the following formula:

wherein R₂ and R₃ in the Chemical Formula (II) are amine moietiesrespectively derived from one selected from the group consisting of thefollowing formulas:

wherein R₄ and R₅ in the Chemical Formula (II) are carboxylic aciddianhydride moieties respectively derived from one selected from thegroup consisting of the following formulas:


13. A liquid crystal alignment agent containing triazine ring basedpolymer expressed by the following chemical formula (III):

wherein R₁ in the Chemical Formula (III) is one selected from thefollowing formula (1a) to (4a):

wherein X in the above formula (1a) is one selected from the followingformula:

wherein Y in the formula (1a) is one selected from the followingformula:

wherein the numerals 1, 2, 3, 4, 5, 6, 7, 8 or 9 in the above formula isone selected from the following formula:

wherein, in the above formula (2a) and (3a), n is 0˜10, and the numerals1, 2, 3, 4 and 5 are respectively selected from the following formula:

wherein Y in the above formula (4a) is one selected from the followingformula:

wherein the numerals 1 and 2 in the above formula (4a) are respectivelyselected from the following formula:

wherein R₂ and R₃ in the Chemical Formula (III) are amine moietiesrespectively derived from one selected from the group consisting of thefollowing formulas:

wherein R₄ in the Chemical Formula (III) is a carboxylic acid moietyselected from the group consisting of the following formulas:

wherein R₅ in the Chemical Formula (III) is a carboxylic aciddianhydride moiety derived from one selected from the group consistingof the following formulas:


14. A liquid crystal alignment agent according to claim 13, wherein thepolymer having the structure of the chemical formula (III) is used as acompatibilizer for suppressing phase separation of polyamide andpolyimide.